INTRODUCTION. vii 



land, added to a continued use of the microscope at 

 home in the examining of our own collections, and re- 

 ferences to the descriptions of others, have, we hope, in 

 many instances enabled us to detect errors in preceding 

 authors, to separate species from varieties, and to dis- 

 cover marks and characters indicative of species in what 

 had been before undecided, or only considered as varia- 

 tions of known individuals. On the form of the leaf 

 undoubtedly much stress is to be laid ; but in the serra- 

 tures, and particularly in the absence or presence, the 

 length, the breadth, and various conformation of the 

 nerves, so much insisted on by Mohr, characters will 

 frequently be found when they fail in almost every other 

 part of the plant. 



But it is not solely on out own investigations that we 

 wish to rely for many of the facts brought forward in 

 these sheets. Many friends both at home and abroad 

 have kindly contributed to us specimens and remarks 

 which have been of great use to us. As however these 

 have been in every instance recorded under the species 

 which by their means have been illustrated, we shall 

 here content ourselves with acknowledging the various 

 liberal communications of Dr. Swartz among foreign 

 botanists, and among those of our country of Mr. Daw- 

 son Turner, whose valuable Herbarium has been freely 

 offered to our use, and whose various communications 

 and corrections have stamped a value on our book which 

 it could not otherwise have possessed. 



Since our main object in the following pages has been 

 to assist the student of Muscology in the investigation 

 of the species of these isles, we have given in the body 

 of the work such generic and specific characters and re- 

 marks upon each as we think necessary for their discrl- 



